The present invention relates to crystal combinations that are resistant to acceleration, and more particularly to those that resist change in their resonant frequency.
As is commonly known, quartz crystals are used to control the frequency of electrical oscillators and in other circuits where an electrical resonant frequency is used. However, a problem with such crystals is that their natural resonant frequency changes with acceleration that may be applied to the crystal. One approach to the problem is shown by D. L. Hammond in the paper entitled "Precision Quartz Resonators" in the Proceedings of the Fifteenth Annual Symposium on Frequency Control, pages 125-138 (1961). This approach used a special mounting for the crystal to reduce the effect of acceleration. In particular, the paper describes two support rings which have six stretched wires to support the crystal. However, the wires are prone to breakage.
Another approach is shown by J. J. Gagnepain and F. L. Walls, "Quartz Crystal Oscillators with Low Acceleration Sensitivity", NBSIR 77-855, National Bureau of Standards (1977). This publication shows two crystals electrically connected in series with one of their axes being anti-parallel oriented. The result of this configuration is that acceleration forces are reduced in the one direction of the anti-parallel oriented axis by about the same amount as in the Hammond configuration.